This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to determine the effect of food containing various amounts of fat on the absorption of oral (taken by mouth) formulation of the male hormone Testosterone (also called T-ester) in the form Testosterone Undecanoate (TU) combined with a lipid (fatty) compound. This will be done by giving the same dose of the study medication to hypogonadal men (men deficient in male hormone testosterone) while changing the amount of fat taken in the diet. Then, amounts of blood testosterone will be measured at different time points in order to see if the amount of dietary fat effects the amounts of testosterone present in blood (Pharmacokinetics study). Although TU is not approved for use in the United States, oral TU has available for treatment of hypogonadal men in Europe, Asia, South America, Australia, Mexico, and Canada for over 30 years. Currently, there are no oral testosterone esters available for hypogonadal men in the United States. 16 men with low levels of blood testosterone will be recruited for the study, and approximately 8 will complete the study at our site. This study will last up to 58 days. There will be 2 outpatient study visits (to determine eligibility for this study) and 5 inpatient hospital stays, each lasting about 28 hours. Potential subjects who are taking testosterone will be withdrawn from testosterone treatment for 1 to 4 weeks prior to entering the study. They should have no other medical problems.